Figure 1.

Structural Outline of Chlorophyll Breakdown with Representative Key Compounds.

In Arabidopsis, chlorophylls are degraded by a known pathway that is commonly present in other higher plant species. Thereby, a pFCC (the C1 epimer of epi-pFCC) that is formed inside senescing chloroplasts is ultimately converted to five NCCs (with different groups R¹ to R³, for example, At-NCC-1, R¹ = CH₃, R² = O-β-glucopyranosyl, and R³ = H), which are derived from isomerization of corresponding FCCs in the vacuole. Relevant catabolite intermediates are depicted along with the enzymes catalyzing their formation. Alternatively, as shown in this work, FCCs are converted by CYP89A9 to FDCCs and the latter isomerize into corresponding NDCCs. As an example, conversion of pFCC to pFDCC and further to pNDCC is depicted. Pyrrole rings (A and B) and relevant atoms are labeled in the structure of pFCC. For abbreviations, see text.